Available phosphorus

The above description of eutrophication has illustrated the complex nature of the problem, particularly in relation to the influence of nutrients, the multiplicity of sources of phosphorus and the spectrum of its bio-availability. Clearly, the most effective long-term solution to many of our eutrophication problems will be to reduce the nutrient load to affected waters. However, it has also been shown that, because the concentrations of available phosphorus required to impose a control on primary production is very low (e.g. 5-10/rgU total dissolved phosphorus), the reduction of nutrients from any one source alone is unlikely to be effective. 

G. A. Gilbert, C. P. Vance, and D. L. Allan. Regulation of white lupin root metabolism by phosphorus availability. Phosphorus in Plant Biology Regulatory Roles in Molecular. Cellular, Organismlc, and Ecosystem Processes (J. P. Lynch and J. Deikman. eds,), American Society of Plant Physiologists, 1998, p. 157. 

Physico-chemical characteristics of the soils were summarized in Table 1. The values were comparable to that described in the previous reports about the SERS (Doi and Sakurai 2003 Doi et al. 2004 Sakurai et al. 1998). The one-way ANOVA indicated that most of the soil variables significantly reflected the land degradation with high values of bulk density, sand content and exchangeable acidity, and low values of moisture content, pH, OM, base (K, Ca, Mg) contents, EC, CEC, base saturation rate, TN and TC contents, available phosphorus and MPN on the glucose medium with no antibiotics. These results also told that the human activities induced several soil environmental gradients. 

Hortenstine CG, Rothwell DF (1973) Pelletized municipal refuse compost as a soil amendment and nutrient source of sorghum. J Environ Qual 2 343-345 Hue NV, Ikawa H, Silva JA (1994) Increasing plant available phosphorus in an ultisol with a yard waste compost. Commun Soil Sci Plant Anal 25 3291-3303 Iyamuremye F, Dick RP, Baham J (1996) Organic amendments and phosphorus dynamics I. 

Two typical acid extractants are the Bray (which has two forms, both of which are acidic) and the Mehlich-3. The Bray extractant is a dilute solution of hydrochloric acid and ammonium fluoride [11], The Mehlich-3 extractant is a dilute solution of acetic and nitric acids and also contains ammonium nitrate and EDTA [11], Both are designed to extract soluble, exchangeable, and easily dissolved nutrients, particularly phosphate. While the Bray extractant is designed to extract plant available phosphorus, the Mehlich-3 extractant also extracts potassium [10-12],... 

Bray RH, Kurtz LT. Determination of total, organic, and available phosphorus in soils. Soil Sci. 1945 59 39 16. 

In a further method [67] for the determination of ammonium lactate extractable (i.e. available) phosphorus in soils, the sample 5g is extracted with 100ml acidic ammonium lactate and then phosphate determined by flow-injection analysis using the stannous chloride method [68]. 

De Pinto [90] measured the rate at which available phosphorus is released from various types of particulates suspended in lake water. The equipment consists of two culture vessels separated by a thin membrane filter, thus facilitating the separation of two particulate suspensions, while at the same time permitting their interaction by diffusion of solutes through the membrane. 

Dorich et al. [91] estimated algae available phosphorus in extracts of suspended sediments. 

Tecator Ltd., Sweden. (1984) Application Note No. ASTN 9ISA. Determination of Available Phosphorus in Soil by Flow Injection Analysis. 

Olsen, S.R., Cole, C.V., Watanabe, F.S. and Dean, L.A. (1954) Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Circular No. 939, US Government Printing Office, Washington, DC. 

Olson, R.A., Rhodes, M.B. and Dreier, A.F. (1954) Available phosphorus status in Nebraska soils in relation to series classification, time of sampling and method of measurement. Agronomy Journal 45, 175-180. 

Sun, L., Gao, Z., Li, L., Yu, X. and Fang, Z. (1981) Determination of soil available phosphorus by flow injection analysis [in Chinese, English translation]. Fenxi Fluaxue (Analytical Chemistry) 9, 585. 

Truog, E. (1930) Determination of the readily available phosphorus of soils. Journal of the American Society of Agronomy 22, 874-882. 

Drying with Phosphorus V) Oxide. If no zeolite is available, phosphorus(V) oxide may be used. Put 500 ml of diethyl ether and 50 g of phosphorus(V) oxide into a one-litre flask provided with a stopper and a calcium chloride tube filled with calcium chloride. Mix the contents of the flask from time to time by carefully shaking it and let the mixture stand for two days. Then pour off the ether from the black oily liquid at the bottom of the flask and distil the ether over metallic sodium. 

The dissolved phosphorus fraction is the most important aquatic phosphorus compartment in terms of biological growth in an aquatic system because it provides the major source of available phosphorus to phytoplankton. To be biologically useful the dissolved phosphorus compounds must... 

Deficiencies of available phosphorus in soils are a major cause of limited crop production. Phosphorus deficiency is regarded by some authorities as the most critical mineral deficiency in grazing livestock. 

PHOSPHORUS (In Biological Systems). Phosphorus is required by every living plant and animal cell. Deficiencies of available phosphorus in soils are a major cause of limited crop production, Phosphorus deficiency is probably the most critical mineral deficiency in grazing livestock. Phosphorus, as orthophosphate or as the phosphoric acid ester of organic compounds, has many functions in the animal body. As such, phosphorus is an essential dietary nutrient. 

The amount that fecal phosphorus levels decline with phytase supplementation will depend on the percentage of phosphorus that is available in the base ration (Yi, 1996b). With available phosphorus at 0.05% of the ration in this study, excretion of phosphorus was reduced by about 25% in pigs receiving phytase compared to the control animals. When the base diet in this study contained 0.16% available phosphorus, excretion was reduced by 50% in pigs receiving phytase but no inorganic phosphorus. 

Although superphosphate fertilizer provides available phosphorus, it is advantageous to provide other needed elements such as nitrogen and potassium at the same time. Thus, diammonium hydrogen phosphate [(NH4)2HP04] provides both nitrogen and phosphorus, while potassium ammonium phosphate [K(NH4)HP04] makes available the three elements most needed in the maintenance of soil fertility. 

Ammonium polyphosphate is one of the most often used phosphoric fertilizers (Corbridge, 1980). It was found to be equally effective when compared with single superphosphate and diammonium phosphate for increasing the yields of wheat and maize and for increasing the available phosphorus content in soil during field experiments (Sharma and Singh, 1998). 

The chemical form of phosphorus in the water column available for uptake by biota is important. The biologically available phosphorus is usually taken to be soluble reactive phosphorus (orthophosphate) , i.e. which, upon acidification of a water sample, reacts with added molybdate to yield molybdophosphoric acid, which is then reduced with SnCl2 to the intensely-coloured molybdenum blue complex and is determined spectrophotometrically (Imax = 882 nm). Reduction in inputs of phosphate, for example from point sources or by creating water meadows and buffer strips to contain diffuse runoff, has obviously been one of the major approaches to stemming eutrophication trends and... 

Table 4.3 Comparison of nitrogen and available phosphorus in the soil and total biomass (aboveplus belowground) for three slope positions in a toposequence in San Carlos de Rio Negro.

One of the first attempts to study soil nutrient dynamics under cultivated pastures in the Amazon basin was conducted in the early 1970s by Falesi (1976). The results of that chronosequence study in different soil types suggested that soil nutrient cycling in pastures differed from that of the traditional slash-and-bum agriculture. The decline in the levels of some nutrients in the soil was found to be more gradual, and the decline in productivity over time in planted pastures could, at least in part, be associated with the behavior of available phosphorus in the soil. 

---